The present invention relates to a mechanical clockwork preferably, but not exclusively, to a clockwork for pocket watches and wrist watches.
Numerous embodiments of clockworks are known. Mechanical clockworks have become increasingly popular in the past few years, whereby synthetic rubies are used for the clockworks in pocket watches, and wrist watches, at locations where a low friction coefficient is needed in order to prevent abrasion, i.e. especially on the bearings of the staffs and in areas of escapement, i.e. in areas of the anchor cooperating with the escape wheel and in areas of the oscillation system (balance wheel) cooperating with the anchor, in particular as bearings for the staff, as anchor plates or anchor jewels as well as impulse pins on the balance staff. This entails additional assembly steps and additional expense.
Furthermore, it is necessary with mechanical clockworks that they be reconditioned at regular intervals in order to restore the accuracy, i.e. especially residue from oil and friction must be washed out and the bearings re-oiled, which also requires at least partial disassembly, of the clockwork, and subsequent re-regulation of the rate.
The object of the present invention is to provide a clockwork that is characterized by high accuracy and in which the customary maintenance heretofore required is practically unnecessary, or necessary only at very large intervals.
xe2x80x9cDLC coatingxe2x80x9d as understood in the present invention refers to Diamond-Like-Carbon hard material coating, which, based on the element carbon forms a diamond-like layer with a high micro-hardness and with an extremely low friction coefficient. The thickness of this coating is, for example, between 2 and 4 mxcexc. The hardness of such a DLC coating is on the order of 2500 HV or higher. It is manufactured by means of plasma-supported chemical gas phase precipitation, for example, at a coating temperature of approximately 150-220xc2x0 C. During precipitation of the coating, silicon and oxygen atoms can also be added, which provides even further reduction of friction. Such a DLC coating and its manufacture is described, for in example, in WO 98/59089.
xe2x80x9cFunctional elementsxe2x80x9d as understood in the present invention are elements of the oscillation system (balance wheel) and the elements of the escapement, in particular, the anchor and the escape wheel. xe2x80x9cFurther functional elementsxe2x80x9d, as understood in the present invention, are also the wheels of the train, the journals and bearings of the clockwork.
As far as the DLC-coated functional elements, plates, or plate elements, made of brass. It is expedient to first apply a thin layer made of a harder metal, for example a chrome layer, to the respective surface in order to achieve better adhesion of the DLC layer.
Functional elements, plates or plate elements, etc. made of steel, in particular stainless steel, are preferably heat-treated, e.g. by means of vacuum hardening or plasma nitriding, before application of the DLC coating.
The present invention makes the use of the heretofore customary press-fit bearing of synthetic ruby unnecessary. The bearings are instead, for example, integrated directly in the plate and the plate elements (bridges) and consist of bearing bores, or preferably of inserted metal bearings, that are DLC-coated at least on their bearing surfaces.
Furthermore, preferably, gear teeth, and pinions together with bearing journals, in the present invention, are DLC-coated, resulting in a significant reduction of friction in the entire train, as compared with conventional clockworks.
In the clockwork, according to the present invention, the bearing journals of the balance staff, and also of the pallet staff, have a larger diameter than in known clockworks, since a DLC coating of these bearing journals and the corresponding surfaces of the bearings provides for very low friction, which enables an increase in the bearing journal diameter without diminishing the function and accuracy. The enlargement of the bearing journal diameter results in improved shock-resistance in addition to making the elements provided for shock resistance in conventional clockworks (spring-mounted bearings for the balance staff) partially, or wholly, unnecessary
A further advantage of a mechanical clockwork is that the anchor pallets, or anchor pins, etc., made of synthetic stones (rubies) are not necessary. This makes the processing steps required for the manufacture of these pallets, stones, etc., and their assembly, unnecessary.
The essential advantages of the present invention can therefore be summarized as follows:
Synthetic press-fit bearings, pallets, anchor jewels, impulse pins etc. made of ruby are no longer necessary.
The clockwork requires no lubrication, so that there is no danger of hardening of oils and the resulting loss of precision.
Reduced friction in the entire system achieves absolutely stable accuracy over an extended period.
Maintenance of the clockwork is practically no longer required, or only after a number of years, for example, after five years.
The high surface hardness prevents mechanical wear due to friction. This increases the long-term precision, as well as the length of the maintenance-free period.
Simplification of the structural design of the clockwork results in a significant reduction in manufacturing costs.
The DLC coating provides protection against corrosion and therefore prevents loss of precision as well as detriments to the overall condition of the clockwork even if penetrated by moisture.
In a preferred embodiment of the present invention, the cooperating surfaces, for example, the bearing surfaces and/or the cooperating surfaces in the area of the escapement, for example in the area of the anchor pallet, are designed in such a way that all of these surfaces possess the DLC coating and the other element of the cooperating surfaces is made of silicon carbide (SiC) . In this way, for example, the bearings of the staffs of the clockwork consist of jewels of silicon carbide, while the surfaces of the staffs cooperating with these jewels possess the DLC coating. In a similar manner, the anchor pallets, for example, are made of silicon carbide, while the surfaces of the anchor or escape wheel 1 cooperating with these pallets are DLC coated. It has been proven that the combination of DLC coating and silicon carbide results in extremely low friction coefficients on the order of 0.05-0.02, very surprisingly, however, since, for example, the combination of silicon carbide and silicon carbide results in a significantly higher friction coefficient, so that silicon carbide is generally to be regarded as unsuitable as a jewel in mechanical clockworks.